The present invention relates to a quartz crystal thermometer of the type wherein a first stable or standard frequency is generated which has a small temperature coefficient, and wherein a second frequency is generated which varies with temperature, for the purpose of being compared to the standard frequency and furnishing a temperature indication.
Quartz thermometers are known wherein two separate quartz elements are provided, one quartz element having a small temperature coefficient or being placed in a nonvariable thermal environment for the purpose of generating a standard frequency, and the other quartz element having a linear temperature coefficient and providing a frequency which varies in accordance with the temperature. One such arrangement is described, for example, in an article entitled "Quartz Crystal Thermometer", by W. H. Wade et al appearing in "The Review of Scientific Instruments", Volume 33, No. 2, February 1962, pages 212 and 213. Another such arrangement is described in the article "Quartz Crystal Thermometer for Measuring Temperature Deviations in the 10.sup.-.sup.3 .degree. to 10.sup.-.sup.6 .degree. C. Range" by W. L. Smith et al appearing in "The Review of Scientific Instruments", Volume 34, No. 3, Mar. 1963 at pages 268 et seq.
In such known arrangements the necessity of using two quartz elements gives them an awkard bulk and results in a high cost. The cost is increased by the fact that the quartz elements used in thermometer arrangements have to have a special cut, which makes them expensive, and the frequency of the two quartz elements must be separately adjusted.
Another disadvantage of these two quartz element thermometers lies in the fact that if the standard quartz element is adjacent the variable quartz element the probe in which they are located has a large thermal inertia and a large volume. Moreover, any difference or deviation of temperature between the two quartz elements distorts the measurement. If, on the other hand, the standard quartz element is exterior to the point where the temperature is to be measured, the influences or disturbing effects are different on the two quartz elements, and the temperature measurement could be erroneous. In that case, a thermal stabilization of the standard quartz element can become necessary, as by placing it in a non-varying thermal environment. Moreover, in using two quartz elements the aging properties of the elements are not the same, with independently changing frequency characteristics, the resulting errors being cumulative.